There have been many attempts made to provide a safer dockplate that can be used not only between surfaces that are relatively even but also between surfaces of different elevations. It is not uncommon when loading or unloading a truck that the loading platform will be of a different elevation or height than the truck cargo surface. To accommodate this difference in height, a bridge is needed that makes the transfer of goods either way (i.e. from truck to dock or visa-versa) as easy as possible.
As early as 1890 U.S. Pat. No. 426,209, issued to McIntyre which disclosed a gangplank that was intended for use as a bridge that would span a ship deck and a dock of different heights. In the McIntyre patent, a three-piece structure is disclosed that has a central main portion A and two toeboards B, one on each end of the main portion A. Toeboards B are connected to main portion A by an easily detachable hook and eye where hooks b' enter eyes a' in the main portion A. The gangplank is disassembled by removing the hook from the mating eye and is intended for rapid attachment and detachment. The bottom portion of the gangplank has projections a and b for lifting all three parts of the gangplank above the surface of the deck and dock. The middle or main portion A of the McIntyre McIntyre structure is used as the bridge, that is, the piece that spans the opening between dock and deck. The toeboards B act as the anchors, one resting on the dock and the other resting on the deck. Since the middle portion A of McIntyre is always used as the bridge, during use excessive angles are formed between the dock toeboard B and the main portion A (see FIG. 3 of McIntyre) which is acceptable for people disembarking from a ship but would be unacceptable for loading or unloading cargo. If, for example, a truck or dolly was being pushed from deck to dock of FIG. 3, there would be a very steep upward incline to overcome and would require a great deal of effort. On the other hand, moving goods from dock to deck or from a loading platform to a truck (in the deck position) a sharp downward incline would occur. Since McIntyre's main portion A and toeboard B are both occupying space on the deck or truck surface, this would take away from the space available for cargo. If the truck or deck was higher than the dock surface of McIntyre, the toeboard B would cause an uneven surface to be formed as will be described in relation to the drawings. Thus, the drawbacks of the McIntyre structure for use in present day situations of truck to loading dock or loading dock to truck are:
a. easy disengagement of toeboards B from the main portion A which could cause a dangerous condition on heavy loads; PA1 b. requirement that main portion A be used as the bridge and thus the resulting steep inclines and angles formed which would make loading and unloading difficult; PA1 c. limitation of cargo space in truck (or deck) caused by the substantial amount of space taken up by the main portion A and all of the lateral dimensions of toeboard B.
In FIG. 3 of McIntyre it is obvious that in the lower righthand surface which would be the truck cargo area, a great deal of space must be occupied by McIntyre's device. Also in McIntyre, platforms on the toeboards which raise the toeboards above the surface provide a convenient gangplank for even surfaces but not particularly suitable for bridging surfaces of uneven heights.
In Baumann U.S. Pat. No. 4,127,201, an unloading ramp is disclosed which is attached to a super-structure of a truck. In Baumann's ramp, it is not possible to transport loads upward, that is, from a truck to a higher elevation. Also, Baumann's device is relatively complex and expensive and cannot be easily moved from one location to another. Because it is attached to a vehicle, it has inherent disadvantages such as portability, simplicity and upward loading use.
In the Agren U.S. Pat. No. 2,449,829, a portable ramp is disclosed wherein the ramp is moved on permanantly attached wheels. Again, the Agren device is relatively complex and expensive. Also, the center plate or portion 8 of Agren must be used as the bridge since the support means 14 is used to hold up center portion 8. If end plates 10 or 10'of Agren was used as the bridge, there would be no support and the end plate would collapse under a load. In order to accommodate different heights or elevations of loading docks or trucks, Agren relies upon a tilting center plate. Again, pushing a heavy load up the center plate incline (as shown in Agren FIG. 3) would involve a great deal of effort.
In Kopp U.S. Pat. No. 4,443,905 a loading ramp is disclosed having a two-plate structure. The plates are hinged by a hinge member having depending feet which hold the two plates slightly elevated along the center hinge portion. Kopp does not disclose a structure having a center or middle baseplate that would remain flat in use and alleviate the presence of steep inclines or angles. Since Kopp has no center plate but rather two folding plates that form a peak when extended, there always exists a gap between the plates. This gap becomes larger in proportion to the length of the feet 44. Thus, when feet 44 are made longer, the gap between plates 22 and 24 of Kopp becomes dangerously large. This gap could become a safety hazard when the feet are lengthened yet if the feet are short, the ramp becomes less convenient for use with platforms of different heights.
In U.S. Pat. No. 3,639,935 to Kumpolt a dock platform having a liftable wing on one side thereof is disclosed. The massive Kumpolt structure could not be used as a loading ramp other than on a dock where it can be readily moved. The complex parts such as hydraulics, coil springs, tri-pedals, etc. make the Kumpolt structure relatively expensive and requires a constant degree of maintenance to keep operational. Any structure such as Kumpolt's with so many moving parts eventually becomes worn and requires replacement parts and repair. There is a need for a simply constructed, efficient ramp having no moving parts, relatively inexpensive and adaptable for use in a multitude of situations.